//https://leetcode.cn/problems/que-shi-de-shu-zi-lcof/description/
class Solution {
    public int takeAttendance(int[] records) {
        int left = 0;
        int right = records.length-1;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (records[mid] == mid) {
                left = mid+1;
            }else {
                right = mid;
            }
        }
        //缺的是最后一个数时
        if(records[left] == left) return left+1;
        return left;
    }
}